1. Field of the Invention
This invention relates to production of mesophase pitch suitable for manufacture of carbon fibers and other carbon artifacts. More particularly, the invention is directed to an improved settling process for separating mesophase pitch from a heat soaked heavy aromatic hydrocarbon feedstock.
2. The Prior Art
There has been a substantial effort in recent years to produce anisotropic pitch comprised of from 40 to 100 percent mesophase, which can then be spun into carbon fibers. One approach to production of mesophase involves heat soaking a heavy aromatic hydrocarbon feedstock at conditions such that a more dense mesophase material forms. Variations of the heat soaking process include sparging inert gas through the feedstock during heat soaking, agitating the feedstock during heat soaking, or a combination of sparging and agitation, as described in U.S. Pat. No. 4,209,500 to Chwastiak.
U.S. Pat. No. 4,317,809 to Lewis et al. describes heat soaking a mesophase precursor material at high pressure, followed by additional heat soaking at atmosphere pressure with gas sparging.
U.S. Pat. No. 4,454,020 to Izumi et al. describes heat soaking mesophase precursor material, separating a heavier anisotropic phase, and further heating the separated portion.
U.S. Pat. No. 4,591,424 to Gomi et al. refers to the use of pressures above atmospheric for heat soaking.
European Patent Application Publication No. 44,714 describes a basic heat soak and gravity separation process for producing mesophase pitch which involves cooling the heat soaked material enough to stop boiling so that settling of mesophase pitch readily occurs.
Many other descriptions of variations of the heat soaking procedure for producing mesophase appear in the literature, and the present invention is applicable in general to any process in which a mesophase forming feedstock is heat soaked to form mesophase and the thus formed mesophase recovered from the heat soaked feedstock. Specific mesophase-forming conditions of temperature, heat soaking time, feedstock composition, gas sparging, agitation and the like have been extensively developed in the prior art, and are not a part of the present invention, as the present invention is generally applicable in any case where a mesophase-forming feedstock is heat soaked and mesophase pitch recovered therefrom, without regard to the specific conditions under which the mesophase is formed.